Glass top plug fuse



. Jan. 1933. s. B. CONDIT 2,104,850

GLASS TOP PLUG FUSE Filed April 16, 1936 waw air/r Patented Jan. 11,1938 UNITED STATES PATENT OFFICE GLASS TOP PLUG FUSE Scars B. Condit,Boston, Mass., assignor to The Chase Shawmut Company,

Newburyport,

12 Claims.

This invention relates to electric fuses of the socalled plug type.

A plug fuse comprises a chambered body of insulating material having anexteriorly screwthreaded metal terminal shell thereon, a center contactmember on one end of the fuse between which and the shell the fuse linkis connected, a window in the end of the plug body opposite the centercontact through which the fuse link can be inspected, and a rim at thetop or window end of the body which is adapted to be grasped between thefingers to screw the fuse into and out of a receptacle.

This invention relates particularly to a plug fuse wherein theinsulating body, the window and the rim are integral and are composed ofglass or equivalent material.

A glass top plug fuse is quite common in the art and large numbers aresold yearly to householders. The public utilities, however, and otherconcerns using and installing fuse plugs that are adapted to be removedand replaced by individuals not in direct control of the concerns arehesitant to use the common glass top fuse because the glass rim isliable to be chipped as by the accidental dropping of the fuse on a hardsurface, so that the fuse presents exposed sharp edges which can cut thefingers of the person removing and replacing this type of fuse in itsreceptacle.

It is an object of the present invention to pro vide a glass top fuse ofsuch nature as to prevent the exposure of chipped or sharp edges to thedirect contact of the fingers of a person rotating the fuse intoor outof its socket or receptacle.

It isa further object of the invention to enclose the finger engageablerim of a glass top fuse with a band of tough material capable ofwithstanding without rupture such impact as might chip or splinter therim enclosed therein to retain the chips or splinters in place and tocover any sharp edges that might be formed, whereby to present a safesurface to be engaged by the fingers.

For some purposes the band is transparent, or substantially so but, whendesired, can have a distinctive color, including black and white, togive a readily visual indication of the capacity of the fuse, one colordenoting, say, a certain range of capacities and another color adifferent range of capacities. A fuse having such a colored bandconstitutes a further object of the invention.

A further object is generally to improve the construction of electricfuses.

Fig. 1 is a side elevation of a glass top plug fuse embodying thepresent invention.

Fig. 2 is a plan view of the fuse of Fig. 1.

Fig. 3 is a longitudinal section taken along line 3-3 of Fig. 1.

Fig. 4 is a plan view of a rim enclosing band prior to its applicationon the rim.

As herein illustrated the fuse comprises a plug body It, having aneXteriorly screw-threaded cylindrical section 52, a peripherallyoutstanding flange or rim M at the upper end thereof, and a transparentwindow 15, the parts l2, l4, and It; being integral and formed of atransparentglass or equivalent material. The plug body has an internalchamber l8 therein which is open at the lower end opposite the window I6. An insulating bushing has an outstanding flange 22 that is seatedupon the end of the plug body and is held in place by an exteriorlyscrew-threaded metal terminal shell 24 that 'is screw-threaded on thescrew threads of the plug body. The bushing 25 has a center contactmember 26 to which one end of a fusible link 28 is electricallyconnected. The other end of the link is connected to the bottom flange39 of the screw shell. The fusible link has a weakened portion 32 thatis adapted to fuse upon overload. Said weakened or readily fusibleportion is disposed under the win- 25 dew IS in position to be viewedthrough the window. The particular fuse herein illustrated is describedand claimed in a copending application of Morris B. Wood, Serial No.18,275 filed April 26, 1935.

In accordance with this invention the rim I4 is protected so that it isnot so liable to chip or splinter when dropped upon a hard surface andthe chips and splinters are retained in close proximity to the body andthe sharp edges resulting from the fractures are enclosed and shieldedfrom contact with the fingers of a person engaging the rim to screw thefuse into or out of its socket receptacle.

The rim protecting means comprises a band or envelope 34 which closelyencircles the rim l4 and has top and bottom parts 36 and 38,respectively, which overlie the top and bottom edges of the rim and theplug faces there-adjoining for a suflicient distance to completelyenclose the region that is liable to present sharp edges when chipped.The band can be composed of a material that is transparent or nearly so,so that light can pass through the band and through the plug bodythereunder and into the link containing chamber l8 to illuminate thelink so that it can be readily viewed through the window l6. However,where the construction of the fuse is such that the link is sufiicientlywell illuminated otherwise, as is herein the case, the band need nothave good light transmitting property and can have a color, includingblack and white, that readily identifies the capacity of the fuse.

The band is in tight non-slipping engagement with the rim and preferablyis shrunk on the rim. The rim is provided with teeth 40 to improve thefinger grip on the rim; and the band when shrunk in place conformsapproximately to the configuration of the teeth so that the banded rimprovides good engagement for the fingers and the teeth hold the band inpositive non-rotating engagement with the rim.

The band is composed of a material sufficiently strong to withstandwithout injury blows that cause the chipping of the glass rim and theband is sufiiciently elastic for this purpose. The band is notmaterially affected by the temperatures to which the fuse is ordinarilysubjected and also is not deleteriously affected by normal moistureconditions. The band preferably is somewhat hydroscopic so as to enhanceits strength under normal conditions of use, although the band when dryhas good strength when in place on the rim.

The band can be formed of any suitable material but preferably iscomposed of a cellulose derivative as cellulose Xanthate or viscose,which is capable of shrinking on drying, so as snugly to conform to theperiphery of the rim. The band can be applied in many ways. The bandforming material can be in a solution. The rim of the fuse may be dippedin the solution and the fuse rotated to apply the solution to theperiphery of the rim. The coated fuse can then be dried to evaporate theliquid and leave a deposit of the material in a band on the rim. It ismore convenient, however, to use a preformed band which can be formed inany suitable manner as by forming a long tube of the material by dippinga mandrel sufficiently repeatedly into a solution of the material, withdryings between each dipping operation, and afterwards stripping thecylinder off the mandrel and cutting the cylinder into bands of suitablewidth. The bands can be stored, until use, in a preservative liquid, aswater, to keep them limp and free from shrinkage.

Fig. 4 illustrates such a band prior to its application on the rim ofthe fuse. The internal diameter of the band preferably is not greatlylarger than the diameter of the rim so that the band will retain itselfon the rim. When the band dries it contracts or shrinks. The shrinkageis relatively great in all directions and for some bands isapproximately 30%. A cellulose xanthate band can have a shrinkage of 30%or more. This relatively great shrinkage causes the band to forciblygrip the rim and to conform to the surface irregularities such as theteeth 63 thereof, and also to cause the edges of the band to draw overand upon the substantially right angularly related faces of the plugbody at the top and bottom edges of the rim.

The band material can be made substantially transparent or nearly so topass light therethrough into the interior of the plug body. The bandalso can be substantially opaque. The lower edge 4'2 of the band isspaced materially above the top edge of the screw-threaded shell 24 sothat there is a clear transparent space 44 around the periphery of theplug body through which light can pass into the interior. Fuses of acertain capacity, or within a certain ran e of capacities, can havebands of one distinctive color, as blue or black, while fuses of acertain other capacity or within a certain other range of capacities,can have bands of a different color as red or white.

I claim:

1. A glass top plug fuse having a closed top plug body provided with atransparent window at one end and a rim that is integral with the bodyand window, said plug body and rim being composed of glass, and aprotective band enclosing and gripping said rim and overlying andenclosing a possible sharp edge thereof and overlying face portions ofsaid body on opposite sides of the rim.

2. A glass top electric fuse comprising a glass body having as integralparts thereof a transparent Window and outstanding rim, and achip-retaining edge-shielding band enveloping and gripping said rim.

3. A glass top electric fuse having a glass body provided with atransparent window and a rim that are integral with the body, said rimhaving a series of projections by which the rim is adapted to be firmlyengaged by the fingers and the fuse rotated, and a protective bandsnugly encircling and enclosing said rim and conformed to the surfaceconfiguration and to said projections thereof.

i. A glass fuse comprising a cylindrical plug body having an integralchamber open at one end, a window closing said other end, an outstandingrim at the window end of said body, an insulating bushing on the openend of said body, a screw-threaded metal terminal shell on said body andoverlying a part of said bushing, a

center contact member carried by said bushing,

a fusible member in said chamber connected between said center contactmember and said terminal shell, said plug body and said rim and windowbeing integral and composed of glass, and a protective band snuglyenveloping and grip ping said rim and overlying a possible sharp edgethereof and overlying face portions of said body on opposite sides ofsaid rim.

5. A glass top plug fuse comprising a one-piece glass body having awindow therein and an outstanding rim integral with said body andwindow, and a chip-enclosing band of electrically insulating materialencircling and enclosing said rim and faces of said body on oppositesides of said rim.

6. A glass top plug fuse comprising a one-piece glass body having awindow therein and an outstanding rim integral with said body andwindow, and a rim-enclosing envelope of electrically insulating materialencircling and enclosing said rim and shrunk thereon.

'7. A glass top plug fuse comprising a one-piece glass body having awindow therein and an outstanding rim integral with said body andwindow, and a band of electrically insulating material encircling andenclosing said rim, said band being composed of a transparent material.

8. An electric plug fuse comprising a plug body having a screw-threadedterminal shell thereon, a center contact member and a fuse linkconnected between said terminal shell and center contact member, saidplug body having a part projecting beyond an end of said terminal shelland said part having a window and an outstanding rim, said plug body,said rim and said window being formed of transparent material of thenature of glass, and a protective electrically insulating envelopeenclosing and gripping said rim, an edge of said envelope being spacedfrom the confronting edge of said terminal shell to provide an uncoveredregion of said transparent body therebetween to admit light into theinterior thereof.

. 9. A glass top plug fuse comprising a glass plug body having integraltherewith a transparent window and an outstanding rim, and a rimprotecting band of tough electrically insulating relatively transparentmaterial encircling and snugly engaging said rim and overlying faceportions of said body on opposite sides of said rim.

10. A plug fuse comprising a plug body having a glass rim, and ashrunk-on rim protective cap of viscose encircling and enclosing saidrim.

11. A plug fuse comprising a glass body having integral therewith a rim,and a colored tough envelope enclosing and gripping said rim.

12. A plug fuse comprising a transparent glass body having a window andoutstanding rim at the top and an internal chamber open at the bottom,an insulating member on the open end of said body, a center contactmember carried by said member, a screw-threaded shell on the exterior ofsaid body, and a colored tough envelope enclosing and gripping said rim,said envelope being terminated short of said shell and there being atransparent section of said glass body exposed between said envelope andshell.

SEARS B. CONDIT.

